Optical compensation sheet, process for producing the same, and polarizing plate and liquid crystal display device using the same

Abstract

A novel optical compensation sheet is disclosed. The sheet comprising a polymer layer formed by coating and, drying a solution comprising a polymer compound and a solvent composition comprising 20% by weight or more of water; and an optically anisotropic layer formed on the surface of the polymer layer by hardening a liquid crystal layer comprising at least one liquid-crystalline compound under irradiation of ionizing radiation at a film surface temperature from 70 to 160° C.; wherein a frontal retardation (Re) value of the optically anisotropic layer is not zero, and the optically anisotropic layer gives substantially equal retardation values for light of a wavelength λ nm coming respectively in a direction rotated by +40° and in a direction rotated by −40° with respect to a normal direction of a layer plane using an in-plane slow axis as a tilt axis (a rotation axis).

1. An optical compensation sheet comprising:
 a transparent substrate, 
 a polymer layer formed on the transparent substrate by coating and drying a solution comprising a polymer compound and a solvent composition comprising 20% by weight or more of water; and 
 an optically anisotropic layer formed on the surface of the polymer layer by hardening a liquid crystal layer comprising at least one liquid-crystalline compound under irradiation of ionizing radiation at a film surface temperature from 70 to 160° C.; 
 wherein a frontal retardation (Re) value of the optically anisotropic layer is not zero, and the optically anisotropic layer gives substantially equal retardation values for light of a wavelength λ nm coming respectively in a direction rotated by +40° and in a direction rotated by −40° with respect to a normal direction of a layer plane using an in-plane slow axis as a tilt axis (a rotation axis); 
 wherein the film surface temperature of the liquid crystal layer, when being irradiated with ionizing radiation, is higher by 1 to 30° C. than the glass transition temperature of the polymer compound, and 
 wherein the liquid-crystalline compound exhibits a cholesteric liquid crystallinity. 
 
     
     
       2. The optical compensation sheet of  claim 1 , wherein the liquid-crystalline compound is a polymerizable liquid-crystalline compound having at least one reactive group, and the optically anisotropic layer is a layer formed by carrying out reaction of the reactive group under heating and/or irradiation of ionizing radiation thereby hardening the liquid crystal layer. 
     
     
       3. The optical compensation sheet of  claim 1 , wherein the solution comprises at least one polymer compound having a polymerizable group in a side chain thereof. 
     
     
       4. The optical compensation sheet of  claim 1 , wherein the liquid-crystalline compound is a polymerizable liquid-crystalline compound having at least one ethylenic unsaturated group, and the optically anisotropic layer is a layer formed by carrying out reaction of the ethylenic unsaturated group under irradiation of polarized ultraviolet light thereby hardening the liquid crystal layer. 
     
     
       5. The optical compensation sheet of  claim 1 , wherein the transparent substrate comprises at least one polymer selected from the group consisting of cellulose based polymers and cycloolefin based polymers. 
     
     
       6. The optical compensation sheet of  claim 1 , used for optical compensation of a liquid crystal cell comprising a pair of substrates disposed facing each other and a liquid crystal layer held between said pair of substrates, comprising a liquid crystal material, liquid-crystalline molecules of said liquid crystal material being aligned substantially normal to the surfaces of said pair of substrates. 
     
     
       7. The optical compensation sheet of  claim 1 , wherein the optically anisotropic layer has a frontal retardation value of 5 to 250 nm. 
     
     
       8. A polarizing plate comprising a polarizing film and at least one optical compensation sheet as set forth in  claim 1 . 
     
     
       9. A liquid crystal display comprising at least one polarizing plate as set forth in  claim 8 . 
     
     
       10. The liquid crystal display of  claim 9 , employing a VA-mode. 
     
     
       11. A process for producing an optical compensation sheet comprising:
 forming, on a transparent substrate, a polymer layer by coating and drying a solution comprising a polymer compound and a solvent composition comprising 20% by weight or more of water; and 
 forming an optically anisotropic layer by irradiating a liquid crystal layer, which comprises at least one liquid-crystalline compound, disposed on the surface of said polymer layer, with ionizing radiation at a film surface temperature of 70 to 160° C. so as to harden it, 
 wherein a frontal retardation (Re) value of the optically anisotropic layer is not zero, and the optically anisotropic layer gives substantially equal retardation values for light of a wavelength λ nm coming respectively in a direction rotated by +40° and in a direction rotated by −40° with respect to a normal direction of a layer plane using an in-plane slow axis as a tilt axis (a rotation axis); wherein the film surface temperature of the liquid crystal layer, when being irradiated with ionizing radiation, is higher by 1 to 30° C. than the glass transition temperature of the polymer compound, 
 and wherein the liquid-crystalline compound exhibits a cholesteric liquid crystallinity.